He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them.
But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion …
...
He must be able to hear them from persons who actually believe them … he must know them in their most plausible and persuasive form.John Stuart Mill

My meagre understanding is that the "seven times for bhikkhus" is in the Vinaya, which is based on an actual case example during the Buddha's time.

Now, for the bhikkhunis, there was no such historical case example for their Vinaya. However, it has become the assumed and default understanding that this means they only have one opportunity. Even though there is apparently no actual explicit statement either way for the bhikkhunis from the Teacher Himself.

(Though I'm very open to evidence to the contrary from the learned.)

My recently moved Blog, containing some of my writings on the Buddha Dhamma, as well as a number of translations from classical Buddhist texts and modern authors, liturgy, etc.: Huifeng's Prajnacara Blog.

In reality, I have never met any monk or nun who had disrobed and re-ordained more than twice in their lives (except the traditional "temporary ordinations" of male Buddhists as seen in Southeast Asia). Have you?